IBM System/360 System Programmer's Manual page 35

Reference
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SV Routine
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Reference Notes
all If your SVC rcutine is to be reenterable, you
cannot use macro-instructions whose expansions
store information into an in-line parameter list.
all You should write SVC routines so that program
interruptions cannot occur. If a program inter-
ruption does eccur during execution of an SVC
routine, the routine loses control and the task
that called the routine terminates.
all
all
If a program interruption occurs and you are
modifying a serially reusable SVC routine, a
system queue, control blocks, etc., the modifica-
tion will never complete; the next time the
partially modified code is used, the results will
be unpredictatle.
You must use the following conventions
~hen
naming SVC routines:
• Types 1 and 2 roust be named IGCnnn; nnn is
the decimal nurrber of the SVC routine. You
rrust specify this
nawe
in an ENTRY, CSECT, or
START instruction.
• Type 3 must te named IGCOOnnn; nnn is the
signed decimal nurober of the SVC routine.
This name must be the name of a member of a
partitioned data set.
• Type 4 must be named IGCssnnn; nnn is the
signed decimal number of the SVC routine, and
ss is the nuwber of the load module minus
one, e.g., ss is 01 for the second load
module of the routine. This naroe roust be the
name of a member of a partitioned data set.
Before your SVC routine receives control, the
contents of all registers are saved. For type 4
routines, this applies only to the first load
module of the routine.
In general, the location of the register save
area is unknown to the routine that is called.
When your SVC routine receives control, the
status of the registers is as fellows:
• Register 0 and 1 contain the same information
as when the SVC routine was called.
• Register 2 contains unpredictable informa-
tion.
• Register 3 contains the starting address of
the communication vector table.
• Register 4 contains the address ef the task
control block (TCB) of the task that called
the SVC routine.